Such a multiple holder has become known from U.S. Pat. No. 4,040,783.
In the prior-art holder, a plurality of test tubes are held in a housing at their respective ends by a holding member which is designed as a plastic disk and is provided with passage openings, through which said test tubes pass. Each opening ends at a receiving device for the test tube. The receiving device is designed in the form of conical recesses around the passage openings. The housing has a bottom with an inlet opening for a gas sample and a cover with a corresponding outlet opening. A gas sample of varying composition is delivered by appropriate delivery means, e.g., a pump, through the test tubes being held between the bottom and the cover. The prior-art multiple holder is used, e.g., to detect the different components of an exhaust gas-air mixture. To do so, test tubes containing different detection reagents are placed into the holder.
The use of the prior-art multiple holder is associated with the disadvantage that the test tubes must be broken or opened at both ends before they are placed in the multiple holder. If, for example, the used test tubes are removed or new test tubes are introduced while the delivery pump continues to operate, the test tube removed last or the new test tube introduced first will be exposed to the stream of gas to be tested for the longest time, whereas the others are exposed to the gas to be tested for different detection times. This can be avoided in the prior-art multiple holder only by stopping the delivery pump to replace the test tubes. However, even in this case test tubes must already be opened and be placed as new tubes into the holder at all times. Foreign or harmful substances may penetrate into the filling of the opened test tubes during this handling and thus they may falsify the test reading during the subsequent analysis of the gas sample.
A measuring arrangement for exhaust gas testing, in which a plurality of test tubes arranged in parallel to one another and branch off from an exhaust gas line, is described in West German Auslegungsschrift No. 21,51,435. The tubes are connected to a pump unit which delivers the exhaust gas sample through the test tubes. When test tubes are introduced, each test tube must be connected to the pump unit in the opened state one by one in the case of this measuring device as well, which leads to different flow-through times of the gas to be tested for each test tube.
In the multiple holder according to West German Patent Specification No. 36,37,869, test tubes equipped with diaphragm closures at their ends are used. A plurality of test tubes are received by one crosspiece. All diaphragm closures of the test tubes introduced are opened simultaneously on joining a connection piece. The test tubes are connected to the delivery pump via the connection piece.
Even though the above-described disadvantages are avoided in this West German Patent 36,37,869, it is not possible to use commercially available test tubes. The test tubes with diaphragm closures must be manufactured specially, and they have the additional disadvantage that they are not sealed as tightly as the test tubes with fused tips and ar damaged more readily.